asteroidcomet

An asteroidcomet is a small Solar System body that exhibits both asteroid-like properties and comet-like activity. The term is informal; in the literature, many such objects are described as active asteroids or main-belt comets, indicating that they occupy asteroid-like orbits yet display transient mass loss.

These bodies can show a coma or a tail while maintaining an asteroid-like orbit. Activity is usually dust-dominated and can be episodic, often occurring near perihelion. Gas production is not always detected, making some objects appear asteroid-like in spectroscopic observations.

The causes are varied: sublimation of subsurface ices, recent impacts that release dust, or rotational disruption that sheds surface material. Some objects may switch between quiescent and active phases across different orbits, complicating the distinction between asteroids and comets.

Notable examples include 133P/Elst-Pizarro, the first recognized main-belt comet, and other cases identified by surveys that link asteroid-like orbits with cometary activity. These objects challenge simple bifurcations between asteroids and comets and demonstrate a continuum of behavior among small bodies.

Studying asteroidcomets helps map the distribution of volatiles in the inner solar system and informs models of how Earth's water and organics could have been delivered. They occupy a niche in small-body taxonomy that crosses traditional classifications and highlights the diversity of solar-system materials.